In recent years, liquid crystal displays (LCD's) have become widely available as computer monitors, television panels, cellular phone screens, and other display applications. Although the price of manufacturing an LCD panel continues to fall, and the energy efficiencies of powering the LCD panel continues to improve, there may be numerous areas of further evolution in energy efficiencies and manufacturing cost reductions for LCD's.
In general, active matrix type liquid crystal display (LCD) devices have an active element (e.g. a thin-film transistor, TFT) on a per-pixel basis for performing switching operations. The LCD controls light transmittance of liquid crystal material in accordance with a video signal so that a picture corresponding to the video signal can be displayed on the LCD panel. The LCD includes an LCD panel having liquid crystal cells arranged in a matrix shape, and driving circuits for driving the LCD panel. In the LCD panel, a plurality of data lines and a plurality of scan lines intersect, and pixel-driving TFT switches are provided at respective intersections. The driving circuits of the LCD include a source driver for supplying signals displaying the picture to the data lines, and a gate driver for supplying signals turning on/off the TFT switches to the scan lines.
One area of design improvement in LCD panels is related to energy inefficiencies arising from inversion methods in LCD's. Dot inversion (i.e. sub-pixel inversion) method has been a pervasive inversion method used in the display industry to provide excellent display qualities for today's LCD panels. Related dot inversion methods used in the industry include, but are not limited to, a dot inversion, a 1+2H dot inversion, 1+alpha*H dot inversion, 1+2V dot inversion, 1+alpha*V dot inversion, alpha*V dot inversion, or alpha*H dot inversion.
However, the dot inversion method consumes substantial amount of power and hampers energy efficiency for a typical LCD panel. If novel scanning and driving methods can be more energy efficient while retaining much of excellent display qualities of the dot inversion method, display manufacturers and consumers may benefit from significant energy efficiency achieved by these novel scanning and driving methods for an LCD panel.
Another area of design improvement in LCD panels is related to backlight unit turn-on time in a field sequential color liquid crystal display (FSCLCD). Field sequential color LCD (FSCLCD) minimizes the power required to produce color images relative to conventional color filter-based LCD's. In one example of an FSCLCD, each 16.67 ms frame is further divided into three equal time intervals, or “sub-frame” of 5.56 ms each.
During each sub-frame, a high-efficiency colored light source is used to backlight the liquid crystal display panel, and different color lights may be turned on per sub-frame. For example, a red light may be turned on for a first sub-frame, a green light may be turned on for a second sub-frame, and a blue light may be turned on for a third sub-frame in sequence.
FSCLCD's may be more efficient than other conventional CF-TFTLCD's because no color filters are used and each color component of the backlight is allowed to pass through the entire pixel area, instead of a mere sub-pixel fraction of each pixel. Because the human eye cannot distinguish these fast changes of colored sequences, it visualizes the colored sequences as integrated colors within each frame. What is perceived is a pixel having the desired composite color and brightness.
In a FSCLCD, access to each cell in the matrix is enabled by a vertical column, with a pulse of such amplitude to produce a desired gray level being applied via a horizontal row. This pulse is used to charge the cell. The charging of cells is performed one gate line (row or column) at a time, from top to bottom or left to right on the matrix at landscape display LCD. The gray levels are set first, followed by the backlighting of the cells that have their gray levels set, using a specific colored LED lamp, then extinguishing of that specific colored LED lamp, followed by resetting of gray levels for the next specific colored LED lamp. Typically, with a three color Red, Green, Blue backlighting system, the light sources or LEDs of one color are interposed with the others as follows: Red, Green, Blue, Red, Green, Blue, Red, etc., resulting in a fairly complex backlighting system.
For the FSCLCD, very fast response time liquid crystal is necessary in general to prevent abnormal color mixing between sub-color sequential periods. The RGB LED turn on time will be very short because LED needs to be turn on after all the pixel data from 1st gate line to last gate line must be written, and transited from one sub-color data to another next sub-color data. The total transition time includes display RGB data writing time which means 2.78 ms when RGB data writing time is ⅙ frame, half of sub-color frame period is the sub-color scanning (writing) time except for LC (liquid crystal)'s transition. Therefore it may be beneficial to increase LED turn on time by reducing the waiting time after sub-color writing time.
Another area of design improvement in LCD panels is related to lowering source driving voltages. In conventional LCD panel designs, a single common electrode in an LCD panel is used for dot (sub-pixel) inversion or similar inversion method to improve optical performance. Because the source driving voltage is around over 6V˜15V or more in these inversion methods, it is not easy to use lower voltage semiconductor fabrication process when fabricating source driver IC. Furthermore, it is hard to integrate source driver block to TCON (timing controller) using lower voltage semicondcutor process. Therefore, methods and apparatuses which lower the source driver voltage and enable lower-cost usage of semiconductor processes for lower voltage IC's may be highly beneficial for cost reductions and energy efficiency.